Optical materials with filtering characteristics have many applications. One of the most obvious is to provide protection against the harmful effects of sunlight. The effects of excessive sunlight on the human body and eye are well known, and in addition exposure to strong sunlight can cause milk to degrade, beer to deteriorate and oil to become rancid. Over-exposure to sunlight is one of the major causes of opthalmic damage, including the formation of cataracts and tissue injury in the retina. Exposure of the body to sunlight can cause sunburn, erythema, skin cancer and premature ageing.
It is known that the damaging effect of light is wavelength dependant. Short wavelength (&lt;400 nm) radiation induces photodegradation of many foods and beverages. Excessive exposure of the body to ultraviolet (UV) light promotes severe deterioration of the epidermis. UV light is also injurious to the eye, and strong blue and green light in the 400-550 nm range is harmful to visual performance. Light with a wavelength longer than 600 nm is generally harmless but can, under certain circumstances cause damage due to its thermal heating effect on the receptor segments in the retinal cells.
Another driving force for developing optical filter materials comes from technological development. Many modern technologies are based on photosensitive materials, for example photoresists for fabrication of integrated-circuit computer chips, photocurable polymer-dispersed liquid crystals for display systems, and colour films for photoimaging processes. Many pharmaceutical and medical products such as drugs, photocurable dental bonding resins, and polymer-based controlled drug delivery devices undergo undesirable photodegradation during storage. In addition many people such as welders, smelters, semi-conductor clean room operators, computer operators and laser operators need to be protected from prolonged exposure to strong and/or constant light emission.